Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease, characterized by premature death of motor neurons in the brain and spinal cord. There is no cure for ALS, necessitating a better understanding of the disease pathogenesis in order to develop effective remedies for this fatal disorder. Most cases of ALS (90%) have no apparent genetic component (referred to as sporadic), whereas ~10% are inherited (familial). Mutations in the Cu/Zn superoxide dismutase (SOD1) gene comprise ~20% of all the familial forms. Sporadic and familial forms of ALS are clinically similar, thus justifyig research on familial ALS to understand sporadic cases. Although the precise cause of ALS remains unclear, evidence suggests that intracellular mutant SOD1 (mtSOD1) aggregates are toxic to motor neurons and neighboring non-neuronal cells, which are also critically involved in the disease. One of the proposed mechanisms for mtSOD1 toxicity involves triggering endoplasmic reticulum (ER) stress and its adaptive signaling transduction pathways, including integrated stress response (ISR). The PERK pathway is central to the ISR, which is a cellular survival mechanism activated by accumulation of misfolded or unfolded proteins in the ER that threaten to overwhelm a cell. The proposed research studies aim to investigate the roles of two prominent ISR components in ALS pathogenesis: PERK (ER kinase) and CHOP (transcription factor involved in stress-mediated cell death). Building upon previous findings that the PERK pathway is protective against mtSOD1-induced ALS, the proposed work will test the hypothesis that an overwhelmed ISR in motor neurons and/or oligodendrocytes, the two cell types that die in ALS, is a major factor that contributes to their demise. The role of the PERK pathway will also be investigated in oligodendrocyte precursor cells (OPCs) and in Schwann cells. To this end, PERK will be genetically deleted from motor neurons, oligodendrocytes, OPCs, and Schwann cells in the mtSOD1 ALS mouse model. Additionally, this proposal will address the role of CHOP in the pathogenesis of ALS and test the hypothesis that its effects are pro-apoptotic. The role of CHOP will be determined in mtSOD1 transgenic mice generated with CHOP deficiency in all cells (global knockout), as well as in distinct cell types, as described above. The mtSOD1 transgenic mice with PERK or CHOP deficiencies will be evaluated for disease progression using clinical and neurological assessment, biochemical analysis of ISR components, histological analysis of cell survival by immunohistochemistry, and ultrastructural analysis of myelin integrity by electron microscopy. Because ER stress is present in sporadic and familial ALS, the proposed research will provide important insights into both forms of the disease. These studies should also help identify the primary cell type involved in ALS, which is critical for development of novel therapeutic approaches, including stem cell transplantation, to prevent motor neuron degeneration in this devastating disease.